The overall objective is to study proteins from biological membranes, so as to gain an understanding to the unique type of physiological function that is mediated by these proteins. The metholology required to bring membrane proteins into solution, where they can be purified and investigated by the traditional methods of protein chemistry, has been developed in previous years. We now propose to study two proteins in detail. One is the Ca ions-activated ATPase form sarcoplasmic reticulum, which is involved in regulation of muscle function. It is an example of an ion pump, mediating active transport of Ca ions. The other protein is rhodopsin from vertebrate visual receptor cells. It is an example of a primary sensory receptor, and the mechanism by which it works may involve light-induced formation of an ion channel through the membrane of the disks in the outer segments of the receptor cell. Work on proteins from human erythrocyte membranes may also be continued.